OBJECTIVE To study prospectively the values of basal and dynamic measurement of inhibin B (INHB), estrodiol (E(2)) following gonadotrophin therapy in vitro fertilization (IVF) cycles in predicting ovarian response to stimulation in young women. METHODS A total of 57 patients younger than 40 years of age undergoing their first cycle of long protocol IVF treatment were studied and serum INHB, E(2) levels were detected on day 3 of the menstrual cycle, before the first administration of gonadotrophin (day 0), on days 1 and 5 after gonadotrophin therapy (day 1, day 5). Ovarian response was presented by: number of oocytes/total rFSH dose and square root of (number of follicles/total rFSH dose). According to number of follicles, number of oocytes and presence or absence of ovarian hyperstimulation syndrome (OHSS), we categorized the results into three different groups: poor response, normal response and OHSS. RESULTS (1) Hormone levels on days 1, 5 of rFSH stimulation: There were positive correlation between INHB (r(S): 0.69 - 0.73), E(2) (r(S): 0.60 - 0.73) and ovarian response (P = 0.000). (2) INHB, and E(2) levels on day 5 of rFSH stimulation were significantly different between poor response, normal response and OHSS groups (P < 0.01), and INHB levels were 164.7, 696.2 and 1263.5 ng/L respectively, and estrodiol levels were 303.2, 1709.5 and 4261.0 pmol/L respectively. CONCLUSIONS Serum INHB, and E(2) levels shortly obtained after gonadotrophin therapy may offer an accurate and early prediction of ovarian response, and INHB response to ovarian stimulation may be a more sensitive and earlier index of ovarian response than estrodiol. Low serum INHB and E(2) levels may predict poor ovarian response; on the other hand, high serum INHB and E(2) levels may predict OHSS.